Field of the Invention
The invention relates to a circuit configuration for generating a controlled output voltage from an uncontrolled input voltage, having a transistor with a load current path connected between an input terminal for supplying the uncontrolled input voltage and an output terminal for picking up the controlled output voltage, and a controlled-gain amplifier for receiving the controlled output voltage, the controlled-gain amplifier having an output terminal being coupled to a control terminal of the transistor.
Voltage controllers are necessary if a supply voltage that can be supplied from outside is subject to major fluctuation, yet function units to be supplied require the most constant possible operating voltage. In order to obtain a large allowable range of fluctuation of the input voltage, so that the supplied function units still work even at the lowest possible input voltage, it is necessary for the voltage drop between the output and the input voltage to be as slight as possible. Such demands are made in the area of motor vehicle electronics, for instance.
Voltage controllers with low voltage loss are described, for instance, in the textbook by Tietze and Schenk, entitled: "Halbleiterschaltungsstechnik" [Semiconductor Circuitry], 9th Edition, 1991, Chapter 18.3.4, pp. 547-549. The load current path of a pnp transistor is connected between the terminal for the uncontrolled input voltage and the terminal for the controlled output voltage, its emitter is connected to the input-side terminal and its collector to the output-side terminal. Nowadays, the function units to be supplied by the voltage controller are typically made with CMOS technology, with which a large scale integration at low cost is possible, with only slight power loss. If the voltage controller is to be disposed together with the function units to be supplied on the CMOS integrated circuit for the sake of the highest possible scale of integration, problems arise in making the control transistor. Producing that kind of bipolar pnp control transistor, that is constructed for high current consumption, is not readily possible using CMOS production processes.
German Published, Non-Prosecuted Patent Application DE 37 16 880 A1 shows a voltage control circuit in which the load current path of an MOS transistor is connected between the input terminal for the connection of an uncontrolled direct battery voltage and the output terminal at which the controlled output voltage for connecting a load is present. A controlled-gain amplifier circuit, to which the controlled output voltage can be supplied, assures triggering of the MOS transistor. The supply voltage of the controlled-gain amplifier is furnished by a voltage chopper circuit, which provides for doubling of the voltage so that the MOS transistor is fully driven.
In the publication Electronic Design, "Microcontroller Switches 5-A, 60-V Current Pulses", Oct. 14, 1993, pp. 71-79, a circuit for triggering MOS transistors is shown in which a high-side switch is triggered by a charge pump. The charge pulse generates a voltage that is above the MOS transistor supply voltage.
German Patent DE 30 10 618 C2 shows a constant voltage circuit in which the emitter-to-collector path of a bipolar transistor having a base terminal that is controlled by a control circuit is located in the input/output current path. A startup circuit assures secure starting up of the circuit. The startup stage includes a capacitor having a first terminal which is connected to the uncontrolled input voltage and a second terminal which is connected to ground through a resistor. The second terminal of the capacitor is also carried through a resistor and a diode to the control circuit.